How to read a peptide COA
A certificate of analysis is only useful if it is batch-specific and method-specific. Here is what to check, in order.
1. Batch linkage
The COA must state a batch or lot number that matches the vial label and the invoice. A COA without a batch number cannot be tied to what you received.
2. Test items and methods
| Item | Method | What "good" looks like |
|---|---|---|
| Identity | ESI-MS / MALDI-TOF | Observed mass matches expected within instrument tolerance |
| Purity | RP-HPLC, UV | Main peak with visible integration; impurity profile stated |
| Water content | Karl Fischer | Stated value, not "N/A" |
| Appearance | Visual | Consistent cake/powder description |
| Sterility (if claimed) | Per method stated | Only claim if actually tested |
3. Chromatogram, not just a number
A purity percentage without the chromatogram is unverifiable. Look at peak shape, integration baseline and whether impurity peaks are shown at all. A suspiciously clean chromatogram with no minor peaks deserves a second look.
4. Signatures and dates
Release date, analyst/reviewer signature and expiry should be present and internally consistent with the manufacture date.
Red flags
- Same COA file reused across different batches or products
- Purity stated to two decimals with no chromatogram
- No batch number, or batch number that does not match the label
- Methods listed as "in-house" with no description
- Certification logos that cannot be verified with the issuing body
Request a sample COA · Why the salt form matters when you read a COA · Writing the specification the COA is tested against · What the certificate's sample does not tell you · The rest of the lot file behind the certificate